An unexpected rhenium(IV)-rhenium(VII) salt: [Co(NH3)6]3[ReVIIO4][ReIVF6]4·6H2O.

The title hydrated salt, tris-[hexa-amminecobalt(III)] tetraoxidorhenate(VII) tetra-kis-[hexa-fluorido-rhenate(IV)] hexa-hydrate, arose unexpectedly due to possible contamination of the K2ReF6 starting material with KReO4. It consists of octa-hedral [Co(NH3)6]3+ cation (Co1 site symmetry 1), tetra-hedral [ReVIIO4]- anions (Re site symmetry 1) and octa-hedral [ReIVF6]2- anions (Re site symmetries 1and ). The [ReF6]2- octa-hedral anions (mean Re-F = 1.834 Å), [Co(NH3)6]3+ octa-hedral cations (mean Co-N = 1.962 Å), and the [ReO4]- tetra-hedral anion (mean Re-O = 1.719 Å) are slightly distorted. A network of N-H⋯F hydrogen bonds consolidates the structure. The crystal studied was refined as a two-component twin.